In casting with an open top casting apparatus, molten metal is introduced into one end of an elongated trough which is arranged above the casting apparatus and has a series of valve openings therein which are spaced apart from one another in a line extending along a parallel to the bottom of the trough, and are in registry with the relatively upper end openings of a series of open ended mold cavities in the casting apparatus which are spaced apart on vertical axes and disposed so that the relatively lower end openings of the respective cavities coincide with a plane parallel to the line of valve openings. The cavities also have a series of bottom blocks telescopically engaged therein at the relatively lower end openings thereof to form sumps within the cavities for the temporary retention of the molten metal therein, and when the molten metal is admitted to the respective cavities at the valve openings corresponding thereto, it forms columns of molten metal upright on the tops of the blocks, and the columns escalate up the axes of the cavities at the surfaces thereof to partially fill the sumps. Then, when the surfaces of the respective molten metal columns have risen to an elevation above the tops of the blocks at which the columns sufficiently fill the sumps to warrant start-up of the casting operation, the casting apparatus and the blocks are reciprocated relatively away from one another along the axes of the cavities to release the columns for travel along the axes, and in the meantime, more molten metal is admitted to the cavities at the series of valve openings to maintain the surfaces of the respective molten metal columns at an operating elevation in which, as the respective molten metal columns cool, they increase their length to form elongated bodies of metal supported upright on the blocks.
Controlling the admission of the molten metal to the cavities during the casting operation has been possible for many years. But being able to also control the admission of the molten metal to the cavities during the fill operation leading up to it, has been a more difficult objective to achieve. This has been true, moreover, even though there has been considerable motivation for being able to do so. The short length molten metal columns which first occupy the sumps during the fill operation, form the so-called "butts" of the bodies of metal or "castings" supported on the blocks. And the formation of a good butt has always been critical to the success of every casting procedure. If the molten metal fills a sump too slowly and solidification of the metal proceeds too rapidly, a "cold joint" or separated butt can occur. This leads to excessive butt scrap, and can be the initiator of other problems as well during the start-up of the casting operation itself. Moreover, if the cooling effect on the lateral faces of a butt is too severe, compared to the cooling effect occurring at the bottom of the butt, the butt can "curl" along its longitudinal axis, and this can also initiate other problems. For one, the weight of the metal at the now unsupported end of the casting, can cause the butt to break down and to initiate cracks which usually propagate up the length of the casting. Or a curled butt can become lodged in the lower end opening of its cavity and to the extent that it is temporarily suspended and unsupported by the block for it. Thereafter, when the butt contracts and drops, the molten metal at the lower end opening of the cavity is dumped into the pit, with the immediate potential for an explosion therein. Or a curled butt can create gaps at the lower end opening of the cavity to the extent that molten metal dumps directly into the pit, again raising the potential for an explosion. And finally, if the conditions under which the butt of a casting is formed, are not properly controlled, unexpectedly high temperatures can occur at the lateral faces of the casting, and can cause hot cracks which may or may not heal at the butt, but more commonly propagate up the length of the casting.
For these and other reasons, the metal casting industry has long sought a process and apparatus with which to exercise control over the admission of the molten metal to the cavities during the entire casting procedure, including the fill operation. In particular, the industry has sought a process and apparatus of this nature which could be used to exercise control on a repeated basis, that is, with uniformly reliable results from one casting procedure to another when multiple procedures are carried out in succession.
Prior to 1985 and for many decades, controlling the admission of the molten metal to the cavities had been accomplished with sets of valve and sensor devices that were operable, respectively, to control the admission of molten metal to the respective cavities at the respective valve openings corresponding thereto, and to sense the elevation of the surfaces of the respective molten metal columns formed in the respective cavities during the casting operation, and to transmit to a control apparatus at signal generation points spaced above the respective surfaces, signals representing the elevations of the respective surfaces. The respective valve devices were suspended from a set of first carrier means that were formed by the corresponding right or left-hand outboard end portions or arms of a set of balance beams that were pivotally mounted on an elongated support fixedly secured to one side of the trough, and that were oriented so as to cantilever the arms over the respective valve openings in the trough and to suspend the respective valve devices in cooperative association with the respective valve openings corresponding thereto. Meanwhile, the opposing outboard end portions or arms of the balance beams were cantilevered over the relatively upper end openings of the cavities, and the respective sensor devices were suspended from them in such disposition above the tops of the blocks as to transmit the respective signals thereof when the molten metal had escalated up the axes of the cavities to the extent of activating the sensor devices. However, the point of activation was not until the fill had been completed. Because of the fixed relationship between the support for the balance beams and the plane with which the relatively lower end openings of the cavities coincided, the beams and the respective valve and sensor devices suspended therefrom, could not exercise control during the fill operation itself. Moreover, the beams and the respective valve and sensor devices could exercise control over the casting operation only if the operating elevation was substantially the same as the start-up elevation. They could not be used to raise and lower the elevation of the surfaces. In short, the control effected was limited to maintaining the operating elevation, and the initial stage of the casting procedure, the fill operation, had to be conducted as a "free fill," that is, as one in which the control effected was exercised by an operator who was trained to prepare for, observe and manipulate the fill operation sufficiently to achieve a crack-free butt and a safe start.
Then, in 1985 and 1986, Takeda et al issued two patents, U.S. Pat. No. 4,498,521 and U.S. Pat. No. 4,567,935, in which their apparatus and technique exercised control over the admission of the molten metal throughout the entire casting procedure, including the fill operation. To do so, they secured the cases of a set of displacement transducers to one side of the trough, suspended a set of float-type sensor devices from the internal displacement components of the set of transducers, and brought in an equal number of so-called electronic "local controllers" that received a set point signal from still another electronic controller, a so-called "master controller," compared the signals transmitted by the respective displacement components of the transducers with the set point signal, and generated from the two the differentials necessary to control the balance of the fill operation after the valve devices had been prepositioned to establish somewhat of a state of equilibrium in the surfaces of the respective molten metal columns during the initial phase of the fill operation.
A subsequent Australian patent Application, No. 17256/92, also disclosed a similar apparatus, and while the Australian and Takeda et al apparatus were effective for the purpose intended, those who employed the respective apparatus found them highly expensive, both to purchase and to maintain, because of the numerous electronic components in them and the fact that in use all of the electronic components were subjected to the intense heat of the casting procedure. Heat is highly deleterious to electronic components and they require close monitoring and maintenance to assure that they will operate reliably from one procedure to the next. It was a principal objective of our invention, therefore, to provide an apparatus and technique-wherein control could be exercised over the entire casting procedure without the use of an undue number of electronic components, and particularly ones which would be exposed to the heat of the casting procedure, and particularly the heat of the trough and that portion of the casting apparatus defining the mold cavities therebelow. We also sought to provide an apparatus and technique of this nature wherein we could fulfill certain other objectives, such as a wider range of control over the casting operation itself, but these will best be explained as our invention is explained more fully hereafter.